The overall objective of the project is to further the understanding of the pathophysiology and etiology of diarrheal states in adults and children. Three inter-related areas of study are being undertaken: 1) validation of a pathophysiologic basis for the secretory diarrheas, and 3) identification of specific etiologic agents responsible for secretory diarrhea. Patients with diarrhea are studied under fed and fasting conditions. All stools are collected and measured for weight, volume, osmolality and electrolyte content. Multiple small bowel biopsies are obtained for the following determinations: nucleotide concentrations, glycolytic enzyme activities, disaccharidase activities, light and electron microscopy and bacterial and viral studies. This approach to diarrhea has several potential benefits. If a pathophysologic classification is validated, the practitioner will be directed toward those pathogenic conditions which elicit the type of diarrhea present in his patients and thus facilitate early diagnosis and management. The elucidation of a common mechanism(s) for secretory diarrhea should provide an understanding of the pathophysiology of diarrheal syndromes associated with excessive secretion. Finally, specific etiologic agents responsible for diarrhea will be correlated with histologic, biochemical, bacteriologic and clinical data.